/*
 * Copyright 2010-2012 Susanta Tewari. <freecode4susant@users.sourceforge.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package bd.org.apache.commons.math.random;

import java.io.Serializable;

/**
 * This abstract class implements the WELL class of pseudo-random number generator
 * from Fran&ccedil;ois Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
 * <p>This generator is described in a paper by Fran&ccedil;ois Panneton,
 * Pierre L'Ecuyer and Makoto Matsumoto <a
 * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
 * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
 * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
 * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.</p>
 *
 * @version $Id: AbstractWell.java 1244107 2012-02-14 16:17:55Z erans $
 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
 * @since 2.2
 */
public abstract class AbstractWell extends BitsStreamGenerator implements Serializable {

    /**
     * Serializable version identifier.
     */
    private static final long serialVersionUID = -817701723016583596L;

    /**
     * Current index in the bytes pool.
     */
    protected int index;

    /**
     * Bytes pool.
     */
    protected final int[] v;

    /**
     * Index indirection table giving for each index its predecessor taking table size into account.
     */
    protected final int[] iRm1;

    /**
     * Index indirection table giving for each index its second predecessor taking table size into account.
     */
    protected final int[] iRm2;

    /**
     * Index indirection table giving for each index the value index + m1 taking table size into account.
     */
    protected final int[] i1;

    /**
     * Index indirection table giving for each index the value index + m2 taking table size into account.
     */
    protected final int[] i2;

    /**
     * Index indirection table giving for each index the value index + m3 taking table size into account.
     */
    protected final int[] i3;

    /**
     * Creates a new random number generator.
     * <p>The instance is initialized using the current time plus the
     * system identity hash code of this instance as the seed.</p>
     *
     * @param k number of bits in the pool (not necessarily a multiple of 32)
     * @param m1 first parameter of the algorithm
     * @param m2 second parameter of the algorithm
     * @param m3 third parameter of the algorithm
     */
    protected AbstractWell(final int k, final int m1, final int m2, final int m3) {

        this(k, m1, m2, m3, null);
    }

    /**
     * Creates a new random number generator using a single int seed.
     *
     * @param k number of bits in the pool (not necessarily a multiple of 32)
     * @param m1 first parameter of the algorithm
     * @param m2 second parameter of the algorithm
     * @param m3 third parameter of the algorithm
     * @param seed the initial seed (32 bits integer)
     */
    protected AbstractWell(final int k, final int m1, final int m2, final int m3, final int seed) {

        this(k, m1, m2, m3, new int[] { seed });
    }

    /**
     * Creates a new random number generator using an int array seed.
     *
     * @param k number of bits in the pool (not necessarily a multiple of 32)
     * @param m1 first parameter of the algorithm
     * @param m2 second parameter of the algorithm
     * @param m3 third parameter of the algorithm
     * @param seed the initial seed (32 bits integers array), if null
     * the seed of the generator will be related to the current time
     */
    protected AbstractWell(final int k, final int m1, final int m2, final int m3,
                           final int[] seed) {

        // the bits pool contains k bits, k = r w - p where r is the number
        // of w bits blocks, w is the block size (always 32 in the original paper)
        // and p is the number of unused bits in the last block
        final int w = 32;
        final int r = (k + w - 1) / w;

        this.v     = new int[r];
        this.index = 0;

        // precompute indirection index tables. These tables are used for optimizing access
        // they allow saving computations like "(j + r - 2) % r" with costly modulo operations
        iRm1 = new int[r];
        iRm2 = new int[r];
        i1   = new int[r];
        i2   = new int[r];
        i3   = new int[r];

        for (int j = 0; j < r; ++j) {

            iRm1[j] = (j + r - 1) % r;
            iRm2[j] = (j + r - 2) % r;
            i1[j]   = (j + m1) % r;
            i2[j]   = (j + m2) % r;
            i3[j]   = (j + m3) % r;
        }

        // initialize the pool content
        setSeed(seed);

    }

    /**
     * Creates a new random number generator using a single long seed.
     *
     * @param k number of bits in the pool (not necessarily a multiple of 32)
     * @param m1 first parameter of the algorithm
     * @param m2 second parameter of the algorithm
     * @param m3 third parameter of the algorithm
     * @param seed the initial seed (64 bits integer)
     */
    protected AbstractWell(final int k, final int m1, final int m2, final int m3, final long seed) {

        this(k, m1, m2, m3, new int[] { (int) (seed >>> 32), (int) (seed & 0xffffffffl) });
    }

    /**
     * Reinitialize the generator as if just built with the given int seed.
     * <p>The state of the generator is exactly the same as a new
     * generator built with the same seed.</p>
     *
     * @param seed the initial seed (32 bits integer)
     */
    @Override
    public void setSeed(final int seed) {

        setSeed(new int[] { seed });
    }


    /**
     * Reinitialize the generator as if just built with the given int array seed.
     * <p>The state of the generator is exactly the same as a new
     * generator built with the same seed.</p>
     *
     * @param seed the initial seed (32 bits integers array). If null
     * the seed of the generator will be the system time plus the system identity
     * hash code of the instance.
     */
    @Override
    public void setSeed(final int[] seed) {

        if (seed == null) {

            setSeed(System.currentTimeMillis() + System.identityHashCode(this));

            return;
        }

        System.arraycopy(seed, 0, v, 0, Math.min(seed.length, v.length));

        if (seed.length < v.length) {

            for (int i = seed.length; i < v.length; ++i) {

                final long l = v[i - seed.length];

                v[i] = (int) ((1812433253l * (l ^ (l >> 30)) + i) & 0xffffffffL);
            }
        }

        index = 0;

        clear();    // Clear normal deviate cache
    }


    /**
     * Reinitialize the generator as if just built with the given long seed.
     * <p>The state of the generator is exactly the same as a new
     * generator built with the same seed.</p>
     *
     * @param seed the initial seed (64 bits integer)
     */
    @Override
    public void setSeed(final long seed) {

        setSeed(new int[] { (int) (seed >>> 32), (int) (seed & 0xffffffffl) });
    }


    /**
     * {@inheritDoc}
     */
    @Override
    protected abstract int next(final int bits);
}
